Moisture is an important issue
Nobody would worry about moisture in wood floors or
concrete slabs, if it would not be for the ugly cupping,
and bowing, milky finishes, mold issues and related
health hazards. Regulations have been established to
avoid mold. Customer complaints have made inspectors and contractors more aware of moisture problems.
Who wants to look at a cupped floor?
For centuries wood has been used in buildings, as structural material, for furniture, floors, moldings, etc. It looks
beautiful and can be shaped easily. It is strong enough
to carry a house on its shoulders and is constantly replenished by our ever-growing forests.
Shrinkage of Red
Oak between 18%
and 6%. At the start
of the test both
pieces ( 1 1/4” x 4”)
had the same size
and 18% moisture
content. The upper
piece dried down to
6%, whereas the
lower piece was
kept at the 18%.
Wood has always been sensitive to moisture. It shrinks
when loosing moisture and expands when absorbing
moisture.
Every board moves differently when the moisture
changes! Shrinkage depends on the pattern of the year
rings. Most shrinkage occurs in the direction of the year
rings. Minimal shrinkage occurs perpendicular to the
year rings. The different shrinkage factors within the same
board cause warpage by pulling the board in different
directions. Quarter-sawn
boards (a) are stable
with very little
shrinkage. Since
only a few quartersawn boards can
be cut out of a round
(a)
tree, these boards
are of high grade
and expensive.
Considering moisture problems, wood floors have always presented a special challenge:
- Tiny changes in each board add up to big changes,
when hundreds of boards are laid side-by-side.
- After installation, all changes in moisture are coming
either from the top or the bottom causing cupping or
crowning. Cupping occurs when the top of the floor
dries out . Crowning
occurs when the
top layer of the floor
absorbs moisture.
well acclimated. Before taking moisture readings check
the manual for necessary wood species corrections.
Temperature corrections may be necessary if the wood
temperature is over 800F or under 600F. When you are
filling out a report make sure the name of the meter,
the wood species and the temperature settings are included.
To avoid problems, all moisture sensitive materials
within the building envelope including the concrete floor
slabs, subfloors and of course the hardwood floor
planks have to be dry. Otherwise, moisture will migrate
into the wood floor until an equilibrium has been
reached. One section being too dry or too wet can influence the entire installation.
Using a Pin Meter with a Slide-Hammer Electrode
Another crucial factor is the relationship between air
humidity and wood moisture. Dry air will pull moisture
out of the wood floor (cupping). Wet air will release
moisture into the wood floor (crowning). These changes
will take place until an equilibrium with the surrounding air has been reached. Following are some examples showing the impact of relative humidity:
Moist summers versus dry winters.
At 700F and 35% rel. humidity, wood moisture will reach 7%.
At 700F and 75% rel. humidity, wood moisture will reach 14%.
At 700F and 20% rel. humidity, wood moisture will reach 5%.
Suggested
moisture
ranges
cabinetry, furniture, wood floors
moldings, window frames
outside painting and sealing
construction lumber below 19%
6-9%
9%
14%
19%
Using a Pin Meter and a Thermo-Hygrometer
Pin meters such as the mini-Ligno E/D are well suited
for checking the moisture in wood floors and subfloors.
Thermo-Hygrometers measure relative humidity and
temperature. Comparing relative humidity and wood
moisture will tell you whether the floor planks are dry
More advanced meters
such as the mini-Ligno
DX/C can be used with a
slide-hammer electrode
and accurately adjusted
for tropical and domestic
species. For the floor inspector the slide hammer
electrode comes in handy
when checking a subfloor
without removing the floor
planks. When measuring
“hard” hardwood floors, it
is easier to hammer the electrode pins into the wood than
pushing the integral pins on the meter into the wood.
Using a Pinless Meter
The advantage of having no pinholes is obvious when
dealing with a customer, who does not want pinholes in
his floor. Pinless meters can easily detect wet spots
and trouble areas in wood floors. To obtain accurate
moisture readings, corrections for wood species are necessary. Pinless meters such as the Ligno-Scanner SDM
have those correction factors built-in. After setting the
wood species, slightly press the meter against the flat
surface. Record moisture readings and wood species
setting. For later reference, you can take a photo with
an identification mark such as a doorframe in the picture.
Then, in case of problems, the same spot can be found
easily and moisture values can be compared with the
original readings. (Temperature corrections are
not necessary for pinless
meters.) The Ligno-Scanner SDM has very unique
calibrations for bamboo.
This is the only meter on
market which has bamboo calibrations.
Helpful Hints
Common Causes for Moisture Problems
-
Floor planks were not dry when installed.
Subfloor was too wet when installed.
Existing or new concrete slab was too wet.
Water spills or leaks.
Ambient conditions see listing on page 2.
Record Keeping and Problem Diagnosis: In case of
complaints the question always comes up, who is to
blame. The problem may be very obvious, but the cause
for the problem is often hard to find:
The home owner turning the air-condition off, the floor
supplier delivering wet floor planks, the installer making mistakes, the contractor not checking the concrete
slab, and so on. Taking moisture measurements and
keeping notes is important at every step until the job is
completed.
Buying Wood Floors: Upon delivery, check the moisture content. Notify the supplier promptly, when the moisture content is not right. If you wait too long, the supplier
may not accept any claims and put the blame on improper storage, while the floor was in your care.
Selectable Measuring Depth in Pinless Meters
The thickness of wood matters for pinless meters. Most
pinless meters are calibrated for a measuring depth of
3/4”. When measuring wood floors less than 3/4” thick, the
measurements will include part of the subfloor or the concrete underneath. This can be avoided by using a meter
such as the Ligno-Scanner SD with selectable measuring
depths 1/4” or 3/4” deep. In addition, the Scanner SD can
be used to check engineered floors thoroughly, because
the top layer can be measured independent from the backing. Choosing the 1/4” depth is also recommended when
checking the dryness of waterborne finishes.
Using the RH Method for Moisture in Concrete
The NWFA Installation Manual states that readings from
non-invasive scan meters or pin meters should not be
used to determine if a concrete slab is dry enough to put a
wood floor down. The in-situ RH test and the Calcium Chloride test are recommended.
Between those two tests, the in-situ probe test is more conclusive because the moisture inside the slab is measured,
whereas the Calcium Chloride test only considers moisture up to 1/4” deep.
Selecting a Wood Species: Not all wood species shrink
the same. Unfortunately, more shrinking is always accompanied by more warping. In entranceways, kitchens or bathrooms, it may be advisable to choose more
stable floor planks of a higher grade to avoid problems.
One rule applies to all floor planks: The more parallel
the grain runs to the edges of the board, the less cupping, crowning or shrinking can be expected. (See pg 1)
Engineered Floors: Not all engineered floors look like
this. Two problems were found in this floor plank and
sorry to say, there was no cure: The floor was manufactured before the top
layer and the backing
were dry. When the
floor planks dried out,
the
multi-layered
backing did not shrink,
but the top layer shrank considerably, pulling the edges
up. The 8” width of the planks made matters worse.
When selecting an engineered floor, consider the width
of the floor planks and the shrinkage factor of the top
layer. The higher the shrinkage factor, the more sensitive the floor will be to moisture changes. The multilayered backing is usually stable.
As always when installing a floor, allow the floor to acclimate and check the moisture top and bottom before
starting the job.
Proper Storage: All floors should be stored in a closedin area with a controlled climate. If stored in a damp
place, dry wood will pick up moisture from the air. Check
relative humidity and temperature in the warehouse, or
other storage areas and compare to the moisture content of the floor planks.
Proper Acclimation: Manufacturers of wood floors and
the NWFA organization suggest allowing time for acclimation before installing a wood floor. During acclimation the room climate should be the same as afterwards when the room is in use.
Seasonal Changes: Depending on the climate in your
area, summers may have a high relative humidity and
winters may have a low relative humidity. Unless a
HVAC is operated year round the moisture in the wood
floor will follow the outside climate. During dry winter
months tiny cracks may appear which disappear during moist summers. As mentioned before the extent of
this “natural” moisture movement depends on wood
species and grade.
If you want to determine the climate changes throughout the year for your area measure the same floor section in your home, shop or office once every month.
After 12 months you have a series of moisture measurements that reflect seasonal changes.
Repair of Moisture Defects: For short moisture intrusions, the damage can be superficial and may disappear after the floor has been dried out to its original
moisture content.
If floor planks were not dry at the time of installation or
absorbed extra moisture later on, the floor may be cupping or crowning. In some cases the floor can be repaired by resanding and refinishing, but only after it
has been confirmed that the floor is dry now.
RH Sensor is inserted into a sleeve and
capped off for acclimation. The cap
can be removed at any time and
a cable can be connected for
moisture readings.
After the test is finished, the cable is connected again to pull the sensor out
of the sleeve. The sensor can be used for further testing.
If defects are so severe that permanent damage to the
structure of the wood has occurred, there is no cure.
The floor has to be replaced. Therefore, moisture problems have to be avoided before they occur.
Measuring the moisture is one important step when
installing floors of lasting beauty.